Three general types of harmonicas have achieved popularity: simple harmonicas, concert harmonicas and chromatic harmonicas. Simple harmonicas typically consist of ten holes or cavities each of which can produce two notes, one drawnote and one blownote. Concert harmonicas have two parallel rows of holes with the reeds in the upper holes tuned one octave higher than those of the lower holes. Both simple and concert harmonicas are tuned to and constructed for a particular key. Chromatic harmonicas, on the other hand, consist in effect of two separate harmonicas, one above the other, in which one instrument is tuned a semitone higher than the other, making it possible to play a single chromatic harmonica in different keys. Chromatic harmonicas, however, suffer from the limitation that players must hunt notes one at a time, and fast chordal groupings are difficult or impossible to play.
In addition to these traditional harmonica types, many specialized harmonicas have been proposed in the prior art. Such specialized harmonicas include those with replaceable reed members with reeds arranged according to preset melodies (U.S. Pat. Nos. 2,595,381 and 2,595,382); harmonicas having means for sharping or flatting the notes (U.S. Pat. Nos. 2,190,633; 2,192,983; and 2,565,100); and harmonicas having means for changing keys (U.S. Pat. Nos. 2,744,434 and 3,580,125). For the most part, such harmonicas are overly specialized and complex, and have not achieved wide-spread acceptance.
The simple ten hole harmonica is a chordal instrument in which the progression of notes (for each key) has long been standardized. The progression, more fully described below, is such that exhaling or blowing across any three adjacent holes will produce a major triad of the keynote and the dominant triad is found by inhaling or drawing. However, other chords are generally unavailable, and the harmonica therefore has a limited range, particularly for improvising and for accompanying many different types of music. In addition, prior simple harmonicas have not been adapted for modal use, a limitation which has further restricted their versatility.